Multi-protocol I/O interconnect time synchronization

ABSTRACT

Described are embodiments of methods, apparatuses, and systems for time synchronization of a multi-protocol I/O interconnect of computer apparatus. A method for synchronizing time across the multi-protocol I/O interconnect may include determining a first local time at a first port of a first switch of a switching fabric of a multi-protocol interconnect and a second local time at a second port of a second switch of the switching fabric, calculating an offset value based at least in part on a difference between the first local time and the second local time, and adjusting the second local time by the offset value. Other embodiments may be described and claimed.

TECHNICAL FIELD

Embodiments of the present disclosure relate generally to multi-protocoltunneling across a multi-protocol I/O interconnect of a computerapparatus.

BACKGROUND

Conventional computer platform architectures include a variety of hostcontrollers to implement a number of different types of I/O betweencomputer platforms and peripheral devices that are connected to theplatforms, and these computer platforms generally includeprotocol-specific connection interfaces that connect to the peripheraldevices via protocol-specific plugs and cables. For example, a computermay include one or more of a USB-specific controller that connects to aperipheral device via a USB-specific connection interface, adisplay-specific controller (e.g., DisplayPort) that connects to aperipheral device via a display-specific connection interface, a PCIExpress®-controller that connects to a peripheral device via a PCIExpress®-specific connection interface, and so on.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure will be described by way ofexample embodiments, but not limitations, illustrated in theaccompanying drawings in which like references denote similar elements,and in which:

FIG. 1 describes a computer apparatus including a multi-protocoltunneling I/O interconnect, in accordance with various embodiments ofthe present disclosure.

FIG. 2 describes a computer system including a multi-protocol tunnelingI/O interconnect, in accordance with various embodiments of the presentdisclosure.

FIG. 3 describes a switching fabric of a multi-protocol tunneling I/Ointerconnect, in accordance with various embodiments of the presentdisclosure.

FIG. 4 describes a protocol stack for a multi-protocol interconnectarchitecture of an I/O complex, in accordance with various embodimentsof the present disclosure.

FIG. 5 describes an implementation of a protocol stack for amulti-protocol interconnect architecture of an I/O complex, inaccordance with various embodiments of the present disclosure.

FIG. 6A describes a physical topology of a domain of switches, and FIG.6B describes an embodiment of a spanning tree for managing the domain ofFIG. 6A, in accordance with various embodiments of the presentdisclosure.

FIG. 7 describes a spanning tree in a domain, in accordance with variousembodiments of the present disclosure.

FIG. 8 describes a format of a route string for routing configurationpackets in a domain, in accordance with various embodiments of thepresent disclosure.

FIG. 9 describes a format of a topology ID configuration register, inaccordance with various embodiments of the present disclosure.

FIG. 10 describes connections that may be established between multipledomains, in accordance with various embodiments of the presentdisclosure.

FIG. 11 describes a multi-protocol tunneling I/O complex andinterconnect, in accordance with various embodiments of the presentdisclosure.

FIG. 12 describes a multi-protocol tunneling I/O complex andinterconnect, in accordance with various embodiments of the presentdisclosure.

FIG. 13 describes a device (e.g., a peripheral device) including amulti-protocol tunneling I/O interconnect connected with amulti-protocol tunneling I/O interconnect, both in accordance withvarious embodiments of the present disclosure.

FIG. 14 describes an architecture for mapping a DisplayPort stream overa multi-protocol switching fabric, in accordance with variousembodiments of the present disclosure.

FIG. 15 describes a structure of a scan line and the packetizationperformed by the DisplayPort IN adapter, in accordance with variousembodiments of the present disclosure.

FIG. 16 describes a link initialization sequence of DisplayPort linktraining, in accordance with various embodiments of the presentdisclosure.

FIG. 17 describes an architecture for mapping an HDMI stream over amulti-protocol switching fabric, in accordance with various embodimentsof the present disclosure.

FIG. 18 describes a video island packet format, in accordance withvarious embodiments of the present disclosure.

FIG. 19 describes a data/control island packet format, in accordancewith various embodiments of the present disclosure.

FIG. 20 describes a time synchronization hierarchy within a singledomain of switches of a multi-protocol switching fabric of various I/Ocomplexes, in accordance with various embodiments of the presentdisclosure.

FIG. 21 describes multiple domains operatively coupled together, inaccordance with various embodiments of the present disclosure.

FIG. 22 describes a model of a switch assumed by various embodiments ofthe time synchronization protocol.

FIG. 23 describes a timestamp measurement model, in accordance withvarious embodiments of the present disclosure.

FIG. 24 describes a time sync packet exchange protocol, which may beused to measure the time offset between the master and slave clocks, inaccordance with various embodiments of the present disclosure.

FIG. 25 describes inter-domain time sync protocol, in accordance withvarious embodiments of the present disclosure.

FIG. 26 describes a topology for time synchronization, in accordancewith various embodiments of the present disclosure.

FIG. 27 is a flow diagram of a method for configuring a multi-protocoltunneling I/O interconnect, in accordance with various embodiments ofthe present disclosure.

FIG. 28 is a flow diagram of a method for operating a computer apparatusincluding a multi-protocol tunneling I/O interconnect, in accordancewith various embodiments of the present disclosure.

FIG. 29 is a flow diagram of a method for time synchronization of amulti-protocol interconnect, in accordance with various embodiments ofthe present disclosure

FIG. 30 describes an article of manufacture having programminginstructions configured to cause an apparatus to practice some or allaspects of multi-protocol tunneling (of the methods of FIGS. 27-29, forexample), in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

Various aspects of the illustrative embodiments will be described usingterms commonly employed by those skilled in the art to convey thesubstance of their work to others skilled in the art. However, it willbe apparent to those skilled in the art that alternate embodiments maybe practiced with only some of the described aspects. For purposes ofexplanation, specific numbers, materials, and configurations are setforth in order to provide a thorough understanding of the illustrativeembodiments. However, it will be apparent to one skilled in the art thatalternate embodiments may be practiced without the specific details. Inother instances, well-known features are omitted or simplified in ordernot to obscure the illustrative embodiments.

Further, various operations will be described as multiple discreteoperations, in turn, in a manner that is most helpful in understandingthe illustrative embodiments; however, the order of description shouldnot be construed as to imply that these operations are necessarily orderdependent. In particular, these operations need not be performed in theorder of presentation. Moreover, methods within the scope of thisdisclosure may include more or fewer steps than those described.

The phrase “in some embodiments” is used repeatedly. The phrasegenerally does not refer to the same embodiments; however, it may. Theterms “comprising,” “having,” and “including” are synonymous, unless thecontext dictates otherwise. The phrase “A and/or B” means (A), (B), or(A and B). The phrase “A/B” means (A), (B), or (A and B), similar to thephrase “A and/or B”. The phrase “at least one of A, B and C” means (A),(B), (C), (A and B), (A and C), (B and C) or (A, B and C). The phrase“(A) B” means (B) or (A and B), that is, A is optional.

FIG. 1 describes a computer apparatus 100 including a multi-protocoltunneling I/O interconnect 108 in accordance with various embodiments.In many embodiments, the computer apparatus 100 may include one or moreprocessors 102. In different embodiments, the one or more processors 102may include one core or multiple cores. In some embodiments, theapparatus 100 may be a multiprocessor system (not shown) where each ofthe processors has one core or multiple cores.

As shown in FIG. 1, the one or more processors 102 may be operativelycoupled to system memory 104 through one or more links (e.g.,interconnects, buses, etc). System memory 104 may be capable of storinginformation that the one or more processors 100 utilize to operate andexecute programs and operating systems. In different embodiments, systemmemory 104 may be any usable type of readable and writeable memory suchas a form of dynamic random access memory (DRAM).

In previously implemented computer apparatuses, an I/O link connecting aperipheral device to a computer system is protocol-specific with aprotocol-specific connector port that allows a compatible peripheraldevice to be attached to the protocol-specific connector port (i.e., aUSB keyboard device would be plugged into a USB port, a router devicewould be plugged into a LAN/Ethernet port, etc.) with aprotocol-specific cable. Any single connector port would be limited toperipheral devices with a compatible plug and compatible protocol. Oncea compatible peripheral device is plugged into the connector port, acommunication link would be established between the peripheral deviceand a protocol-specific controller.

In the computer apparatus as described in the embodiment shown in FIG.1, the one or more processors 102 may be operatively coupled to an I/Ocomplex 106, which may house one or more multi-protocol I/Ointerconnects 108 configured to control one or more I/O links that allowthe one or more processors 102 to communicate with one or more I/Operipheral devices 110. For providing the multi-protocol capability, atleast in part, the I/O interconnect 108 may include a multi-protocolswitching fabric 114 configured to carry multiple I/O protocols. Invarious embodiments, the multi-protocol switching fabric 114 maycomprise a plurality of cross-bar switches. Examples of I/O peripheraldevices 110 may include a display device, a keyboard device, anexpansion port, a desktop or mobile computer system, or a router, amongother devices.

A non-protocol-specific connector port 112 may be configured to couplethe I/O interconnect 108 with a connector port (not shown) of the device110, allowing multiple device types to attach to the computer system 100through a single physical connector port 112. Moreover, the I/O linkbetween the device 110 and the I/O complex 106 may be configured tocarry multiple I/O protocols (e.g., PCI Express®, USB, DisplayPort,HDMI®, etc.) simultaneously. In various embodiments, the connector port112 may be capable of providing the full bandwidth of the link in bothdirections with no sharing of bandwidth between ports or betweenupstream and downstream directions. In various embodiments, theconnection between the I/O interconnect 108 and the device 110 maysupport electrical connections, optical connections, or both.

The apparatus 100 may be a stand-alone device or may be incorporatedinto various systems including, but not limited to, various computingand/or consumer electronic devices/appliances, such as desktop computingdevice, a mobile computing device (e.g., a laptop computing device, ahandheld computing device, a tablet, a netbook, etc.), mobile phones,smart phones, personal digital assistants, servers, workstations,set-top boxes, digital reorders, game consoles, digital media players,and digital cameras. A block diagram of an example system 200 isillustrated in FIG. 2. The system 200 may comprise one or moreprocessor(s) 202, system memory 204, and an I/O complex 206, alloperatively coupled by a bus 115. The I/O complex 206 may include one ormore multi-protocol I/O interconnects 208, each of which include aswitching fabric 214 and control one or more I/O links that allow theone or more processors 202 to communicate with one or more I/Operipheral devices 210. In various embodiments, the system 200 may havemore or fewer components, and/or different architectures.

The system 200 may include communications interface(s) 217 operativelycoupled to the bus 215 to provide an interface for system 200 tocommunicate over one or more networks and/or with any other suitabledevice. The communications interface(s) 217 may include any suitablehardware and/or firmware. The communications interface(s) 217 for oneembodiment may include, for example, a network adapter, a wirelessnetwork adapter, a telephone modem, and/or a wireless modem. Forwireless communications, the communications interface(s) 217 for oneembodiment may include a wireless network interface controller 219having one or more antennae 221 to establish and maintain a wirelesscommunication link with one or more components of a wireless network.The system 200 may wirelessly communicate with the one or morecomponents of the wireless network in accordance with any of one or morewireless network standards and/or protocols.

The system 100 may include a display device 223, such as, for example, acathode ray tube (CRT), liquid crystal display (LCD), light emittingdiode (LED), or other suitable display device, operatively coupled tothe bus 215 for displaying information. In various embodiments, thedisplay device 223 may be a peripheral device interconnected with thesystem 200. In various ones of these embodiments, such a peripheraldisplay device may be interconnected with the I/O complex 206 by way ofthe multi-protocol port 212.

As described herein, for providing an I/O interconnect capable ofcarrying multiple I/O protocols, one or more of the various I/Ointerconnects described herein may include, among other things, amulti-protocol switching fabric 314 comprising a plurality of cross-barswitches, as shown in FIG. 3. The multi-protocol switching fabric 314may be similar to other multi-protocol switching fabrics describedherein. In general, the switches 316 a, 316 b are devices comprisingmultiple ports 320 s, 320 b, 322 a with the ability to route a packetfrom any input port to any output port. In various embodiments, theswitches 316 a, 316 b may comprise any number of ports 320 s, 320 b, 322a, with each additionally including an internal control port 326 a, 326b. The switches 316 a, 316 b may each optionally include a timemanagement unit 330 a, 330 b for use in distributing and synchronizingtime throughout the multi-protocol switching fabric 314, as describedmore fully herein.

Switch 316 a may represent a first type of switch including null ports320 a configured to connect to a single optical or electrical link,while adapter ports 322 a may be configured to connect to one or moremapped I/O protocol links. The adapter ports 322 a may be used toconnect mapped I/O protocol entities to the multi-protocol switchingfabric 314. As used herein, the term “adapter” may be used to refer tothe protocol adaptation function that may be built into the switch portto encapsulate the mapped I/O protocol packets into I/O packets thatflow over the multi-protocol switching fabric 314.

Switch 316 b may represent a second type of switch including only nullports 320 b (like null ports 320 a) configured to connect to a singleoptical or electrical link.

Although the switches 316 a, 316 b depicted in FIG. 3 each include fouradapter ports 322 a and four null ports 320 a, 320 b, the actual numberof ports 320 a, 320 b, 322 a may be fewer or more than that shown. Inorder to provide connectivity between switches 316 a, 316 b, a switchimplementation generally minimally includes either at least one nullport and at least one adapter port, or at least two null ports.

In various embodiments, the multi-protocol switching fabric 314 maycomprise one or more of the first type of switches 316 a and one or moreof the second type of switches 316 b.

For implementing various multi-protocol tunneling between adapter portsof a switching fabric within the scope of the present disclosure, aconnection manager (not illustrated) may be provided. The connectionmanager may be implemented in software, firmware, as logic within an I/Ocomplex, as part of a system BIOS, or within an operating system runningon a computer apparatus or system in which the I/O complex is included.

An example protocol stack for the multi-protocol interconnectarchitecture of an I/O complex is shown in FIG. 4. The electrical andoptical sublayers, the logical sublayer, the transport layer, and theframe layer may define the base multi-protocol interconnect architectureof the I/O complex, in which the physical layer comprises theelectrical, optical, and logical sublayers. The mapped protocol layersmay describe the mapping of the specific I/O protocols onto themulti-protocol interconnect architecture.

In various embodiments, and with reference to FIG. 3 and FIG. 4, thetransport layer may be implemented by all ports 320 a, 320 b, 322 a ofthe switches 316 a, 316 b of the multi-protocol switching fabric 314,the physical layer may be implemented by all null ports 320 a, 320 b,and the adapter ports 322 a may implement a single mapped protocol layeror the frame layer.

An example implementation of the protocol layering is shown in FIG. 5.In the example shown, two protocols are implemented using switches 516a, 516 b, 516 c, 516 d. Each of the switches 516 a, 516 b, 516 c, 516 dinclude control ports 526 a, 526 b, 526 c, 526 d, and time managementunits 530 a, 530 b, 530 c, 530 d.

As shown, the adapter ports 522 a 1, 522 c implement a first protocollayer (or frame layer) “protocol 1,” and adapter ports 522 a 2, 522 dimplement a second protocol layer (or frame layer) “protocol 2.” Allports implement the transport layer, while the physical layer isimplemented by all null ports 520 a, 520 b, 520 c, 520 d.

As such, a link (e.g., link 532) between ports of switches mayeffectively be shared by multiple paths traversing the fabric betweenadapter ports of the multi-protocol switching fabric. In variousembodiments, the multi-protocol interconnect architecture may beconnection-oriented such that a path is configured end-to-end beforedata transfer takes place. The path may traverse one or more linksthrough the multi-protocol switching fabric, and each hop, the path maybe assigned a locally unique identifier that may be carried in theheader of all the packets that are associated with the path. In variousembodiments, packets belonging to the path may not be reordered withinthe multi-protocol switching fabric. Buffer allocation (flow control)and Quality of Service may be implemented on a per-path basis. As such,a path may provide virtual-wire semantics for a mapped I/O protocolacross the multi-protocol switching fabric.

In various embodiments, the physical topology of a collection ofswitches (a domain) may be an arbitrarily interconnected graph. FIG. 6Ashows an example of a physical topology of a domain of switches 1-6. Itshould be noted that a domain is a management concept rather than anoperational one. In various embodiments, a connection manager, asdescribed earlier, may configure the domains of a switching fabric. Forfurther management purposes, a multi-protocol apparatus may beconfigured to create a spanning tree (by way of the connection manager,for example). FIG. 6B shows an example spanning tree created formanaging the domain of FIG. 6A in which the switch 1 at the top of thespanning tree may be referred to as the root switch. It is noted that aspanning tree may include any suitable number of levels. In variousembodiments, the maximum number of levels of the spanning tree may beseven.

FIG. 7 shows an example of a spanning tree in a domain. Also shown areexample assignments of unique topology IDs to each of the switches inthe domain. For example, switch J has a topology ID of 0,4,1,1,2,1,8. Invarious embodiments, unique topology IDs may be assigned to every switchof a domain and each topology ID may represent the position of theswitch within the spanning tree of the domain. In various embodiments,the assignment of the topology IDs may be done by the connection managerduring initialization in which the domains may be created by enumeratingthe switches that are reachable and the topology IDs may be assigned foreach switch.

As shown in FIG. 7, the domain includes seven levels (levels 0-6), andthe topology IDs of each of the switches are sequences of seven portnumbers representing the egress ports at each level of the tree on thepath, from the root switch to itself. The topology ID of a switch at adepth of X (where X is from 0 to 6 in this example) may contain anon-zero port number for levels 0 to X−1. The port number at depth X maybe 0 denoting the control port of the switch at depth X. The portnumbers from depth X+1 to 6 may be treated as “don't care” and may beset at 0. Thus, in the example shown, the control port at the rootswitch has a topology ID of 0,0,0,0,0,0.

In various embodiments, the routing of configuration packets flowingdownstream (in relation to the spanning tree) may be based on thetopology ID of the target switch. The configuration packets may berouted in the transport layer packet header. In various embodiments,configuration packets flowing upstream may not use the topology ID andmay simply be forwarded over the upstream port of each switch.Typically, every configuration packet carries a route string included inits payload. An example format of the route string is shown in FIG. 8.As shown, the route string may essentially be the topology ID of theswitch to which the configuration request is sent or from which theconfiguration response originates. The MSB bit (CM bit) of the routestring may be set to 0 when the configuration message is flowingdownstream (from the connection manager to the switch) and set to 1 ifthe message is flowing in the upstream direction.

In various embodiments, each switch may be configured with its topologyID and its level in the spanning tree by the connection manager. Eachswitch may also be configured with the port number that points upstreamto the connection manager of the domain either through hardwarestrapping or other similar mechanisms. In various embodiments, thetopology ID, depth (in the tree), and upstream facing port may beconfiguration registers in the switch configuration space of everyswitch that are initialized by the connection manager duringenumeration. An example format of the topology ID configuration registeris shown in FIG. 9. For the illustrated example, the MSB of the topologyID may be a valid flag, which may be set to 0 on reset and set to 1 bythe connection manager when the topology ID is initialized. The reservedbits of the topology ID may be set to 0.

Configuration packets flowing down the tree may be routed by the controlport of a switch in accordance with one or more rules. For example, invarious embodiments, the control port of the switch may be required toextract the port from the route string that corresponds to itsconfigured level in the tree. In various embodiments, if the port is 0,the control port may be required to consume the packet. In variousembodiments, if the port is non-zero, the control port may be requiredto forward the packet over the switch port that matches the portextracted from the route string. In various embodiments, configurationpackets flowing up the spanning tree may simply be forwarded over theconfigured upstream facing port.

Multiple domains may interconnected in various embodiments. FIG. 10shows example connections that may be established between multipledomains. As shown, switches 1-6 of Domain 1 may be interconnected withswitches A-E of Domain 2.

In various embodiments, inter-domain links may be discovered either whenthe connection manager performs the initial discovery of the topologyfollowing power-on or by processing a hot-plug event. A link may bedesignated to be an inter-domain link when a read of the switchconfiguration space of the switch across the link results in an ERRORpacket being sent that shows that the topology ID field has beenpreviously assigned. When an inter-domain link is discovered, theconnection manager may notify system software. The mechanism used todeliver the notification may be implementation-defined.

In various embodiments, the transport layer may only define the routingof inter-domain configuration packets between the two connectionmanagers of the domains that are connected by an inter-domain link.Routing of configuration packets across multiple domains may becontrolled by system software. When domains are daisy-chained,configuration packets passing from the originating domain may bedelivered to the connection managers of every domain along the path tothe target domain. The connection managers of the intermediate domainsmay pass the configuration packets to the system software which may beresponsible for relaying the packet across the inter-domain link towardsthe target domain.

The routing of inter-domain REQUEST packets may be in accordance withone or more rules. For example, in various embodiments, system softwareon the originating domain may form REQUEST packet with a route stringthat points to the egress port of the domain that connects to theinter-domain link over which the packet must be forwarded and the CM bitmay be set to 0. The packet may be required to be routed based on theroute string at each hop within the domain and forwarded over the egressport across the inter-domain link. At the ingress port of the receivingdomain, the control port may remap the route string to point to theingress port over which the packet was received and the CM bit may beset to 1. In various embodiments, the packet may then be required to berouted to the connection manager of the receiving domain like otherintra-domain configuration packets. The packet may be required to bedelivered by the connection manager of the receiving domain to systemsoftware.

The routing of inter-domain RESPONSE packets may follow one or more ofthe same steps above. In various embodiments, system software thatconstructs the RESPONSE packet may use the route string in thecorresponding REQUEST packet with the CM bit set to 0.

In various embodiments, the transport layer may employ a hierarchical,credit-based flow control scheme with respect to flow through themulti-protocol switching fabric to prevent or minimize overflow ofreceive buffers due to congestion. In various embodiments, the flowcontrol scheme may allow a receiver to implement various bufferallocation strategies ranging from dedicated buffers per-path to sharedbuffer pools that are dynamically shared by multiple paths. In variousembodiments, flow control may be turned off on a per-path basis. Whenflow control is turned off for a path, the path may be required to beprovisioned with a receive buffer that can hold at least one maximumsized transport layer packet at each link.

FIG. 11 shows an example I/O complex 1106 in accordance with variousembodiments. I/O complex 1106 may be similar to the I/O complex 106 ofFIG. 1, including an I/O interconnect 1108 configured to couple with adevice 1110. The device 1110 may be configured with one or more I/Oprotocols (e.g., PCI Express®, USB, DisplayPort, HDMI®, etc.).

In various embodiments, the I/O complex 1106 may be configured toconnect the device 1110 with one or more protocol-specific controllers1109 a, 1109 b, . . . 1109 n via the I/O interconnect 1108 in order totunnel multiple I/O protocols over a common link in a manner that istransparent to the OS software stacks of tunneled I/O protocols. Theprotocol-specific controllers 1109 a, 1109 b, . . . 1109 n may beconfigured to then communicate with respective protocol-specific driversin the OS for configuring the device 1110 as if the device 1110 wasdirectly connected with the protocol-specific controller 1109 a, 1109 b,. . . 1109 n.

FIG. 12 shows an example hardware and software implementation of amulti-protocol apparatus (such as apparatus 100 of FIG. 1, for example)configured to tunnel multiple I/O protocols over a common link in amanner that is transparent to operating system software stacks oftunneled I/O protocols. In various embodiments, a multi-protocolapparatus may employ a multi-level hot-plug signaling scheme to supportthe tunneling of multiple I/O protocols over a common interconnect in asoftware-transparent manner.

For the implementation shown in FIG. 12, an I/O hot-plug indication maybe sent by the I/O interconnect 1208 to the I/O driver in the OS (or toembedded I/O firmware) when the device 1210 is plugged into thenon-protocol-specific connector port 1212 of the apparatus 1200. Thehot-plug indication may then be processed by the I/O driver 1213 in theOS/firmware, resulting in communication path(s) being establishedbetween the I/O interconnect 1208 and the device 1210. In variousembodiments, establishing communication path(s) may include configuringone or more paths between a source adapter and a destination adapter ina domain (described more fully elsewhere). Once the path(s) areestablished, mapped I/O protocol-specific configuration may be performedin which a protocol-specific hot-plug indication may be sent by theassociated protocol-specific controller 1209 a, 1209 b, . . . 1209 n tothe respective protocol-specific driver 1211 a, 1211 b, . . . 1211 n inthe OS/firmware. The protocol-specific driver 1211 a, 1211 b, . . . 1211n may then configure the associated protocol-specific controller 1209 a,1209 b, . . . 1209 n as if the device 1210 was directly connected withthe protocol-specific controller 1209 a, 1209 b, . . . 1209 n. At thispoint, the peripheral device 1210 may be visible to system software andconfigured to be used by applications.

In various embodiments, the apparatus 1200 may be configured such thatwhen the device 1210 is disconnected from the port 1212, a reversesequence of events may occur. Specifically, the protocol-specificdrivers 1211 a, 1211 b, . . . 1211 n may process the protocol-specificunplug event, and then after the protocol-specific processing, the I/Odriver 1213 may process the I/O unplug event.

Peripheral devices described herein (device 110, 210, 1110, or 1210, forexample) may be any one of various types of devices, as noted earlier.In various embodiments, the peripheral device may be an expansion port(or other multi-protocol peripheral device) with which one or more otherdevices, with one or more I/O protocols, may be coupled. For example,for embodiments in which the peripheral device is an expansion port, thedevice may be simultaneously coupled with a PCI Express® device and aDisplayPort device, which may be coupled with an I/O complex through theexpansion port device. In another example, the peripheral device may bea mobile or desktop computer system and one or more other devices may becoupled with the mobile or desktop computer system and with the I/Ocomplex through the device. In various embodiments, multiple peripheraldevices may be coupled together by daisy chaining the devices together.

In various embodiments, the peripheral device and/or the other devicescoupled with the peripheral device may also include an I/O interconnectsimilar to one or more of the I/O interconnects 108, 208, 1108, 1208described herein. As shown in FIG. 13, for example, a device 1310including a multi-protocol interconnect 1301, which in turn includes amulti-protocol switching fabric 1303, may be configured to beinterconnected with a multi-protocol apparatus 1300 which also includesa multi-protocol interconnect 1308 and switching fabric 1314. One ormore other peripheral devices 1305 a, 1305 b, . . . 1305 n may beinterconnected with the I/O interconnect 1301 via one or morecorresponding non-protocol-specific ports 1312.

As noted herein, various embodiments of I/O complexes and apparatusesincluding I/O complexes may be configured to tunnel a multiple protocolsacross a multi-protocol interconnect in a software-transparent manner orsubstantially transparent manner. Specific examples of DisplayPort andHDMI® tunneling techniques will now be described in further detail withreference to FIGS. 14-19.

FIG. 14 shows an example architecture for mapping a DisplayPort streamover a multi-protocol switching fabric described herein. Thearchitectural model used for mapping DisplayPort may be that of avirtual wire between the DisplayPort source and the DisplayPort sink.The DisplayPort map may behave as a DisplayPort cable replacement andmay therefore be completely transparent to the DisplayPort link from asource and sink (and software stack). The DisplayPort IN adapter mayterminate a DisplayPort link from a source device and encapsulateDisplayPort main link and AUZ channel transmissions inside packets andtransport them across the switch network. At the other end of thenetwork, a DisplayPort OUT adapter may decapsulate the video and AUXchannel data and recreate a DisplayPort link that connects to a sinkdevice. Hot plug detect (HPD) indications may also be transmitted aspackets.

In various embodiments, when a DisplayPort link is mapped onto amulti-protocol switching fabric described herein, the continuous mainlink data stream may be converted into multiple types of I/O packets.FIG. 15 shows an example structure of a scan line and the packetizationperformed by the DisplayPort IN adapter. During the packetization, allthe stuffing symbols (within a transfer unit TU of active pixel data andduring the blanking periods) may be discarded by the DisplayPort INadapter and may be recreated by the DisplayPort OUT adapter. In order toenable accurate reconstruction of the stuffing at the DisplayPort OUTadapter, the DisplayPort IN adapter may include with each I/O packet aFill Count field that may specify the number of stuffing symbols thatwere discarded immediately preceding the current packet as shown.

In various embodiments, AUX channel requests may be packetized and sentas I/O packets across the multi-protocol switching fabric by theDisplayPort IN adapter and may be replayed by the DisplayPort OUTadapter at the other end. AUX channel responses may be packetized andsent as I/O packets across the multi-protocol switching fabric by theDisplayPort OUT adapter and may be replayed by the DisplayPort INadapter at the other end.

In various embodiments, HPD indications may be packetized and sent asI/O packets across the multi-protocol switching fabric by theDisplayPort OUT adapter and may be replayed by the DisplayPort INadapter at the other end.

DisplayPort link training may be initiated by a graphics processing unit(GPU, not illustrated) over the AUX channel and may be carried out insuch a way that the DisplayPort links between the GPU and theDisplayPort IN adapter and between the DisplayPort OUT adapter and thedisplay device get trained to the same configuration. In variousembodiments, this may result in that from the GPU perspective, displaydevice hot-plug and uplug operations may be supported in the same wayfor a display device connected across a multi-protocol switching fabricas for a display device attached locally to the GPU. An example linkinitialization sequence is shown in FIG. 16 in which training fails atthe first attempt and the DisplayPort OUT adapter is forced to select areduced bit-rate configuration.

The DisplayPort tunneling architecture described herein may supporttransparent tunneling of premium content streams over a multi-protocolswitching fabric described herein. The multi-protocol switching fabricmay appear as a DisplayPort virtual wire directly connecting aHigh-bandwidth Digital Content Protection (HDCP) transmitter to a HDCPreceiver. The HDCP content protection mechanisms may be handledtransparently by the multi-protocol switching fabric.

FIG. 17 shows an example architecture for mapping an HDMI stream over amulti-protocol switching fabric described herein. The architecturalmodel used for tunneling HDMI may be that of a virtual wire between anHDMI source and an HDMI sink. The HDMI tunnel may behave as an HDMIcable replacement and may therefore be transparent to the HDMI sourceand sink (and to the software stack). As shown in FIG. 28, the HDMI INadapter may terminate an HDMI link from a source device and encapsulateHDMI TMDS link and DDC channel transmissions inside I/O packets andtransport them across the switch fabric network. At the other end of thenetwork, an HDMI OUT adapter may decapsulate the TMDS and DDC channeldata and recreate an HDMI link that connects to a sink device. HPDindications may also be transmitted as I/O packets.

In various embodiments, when an HDMI link is mapped onto amulti-protocol switching fabric described herein, the continuous TMDSlink A/V stream may be converted into multiple types of I/O packets. A“video island packet” (carries pixel data) may be used to transport theactive pixel data across the multi-protocol switching fabric from theHDMI IN adapter to the HDMI out adapter. Data/control island packets maybe used to transport the data and control characters from the HDMI INadapter to the HDMI OUT adapter. Example video island packet anddata/control island packet formats are shown in FIGS. 18 and 19respectively.

In various embodiments, the HDMI IN adapter may act as a proxy slavedevice on the bus. The HDMI IN adapter may receive the DDC transactionparameters sent by the HDMI Source and transmit them through the DDCpath to the HDMI OUT adapter using a DDC request packet. The HDMI OUTAdapter may act as a proxy master device on the bus and initiate the DDCtransaction to the HDMI Sink. When the HDMI Sink responds with data oracknowledgement, the HDMI OUT adapter may transmit the response to theHDMI IN adapter using a DDC response packet. When the HDMI IN adapterreceives the DDC Response packet, the HDMI IN adapter may relay thetransaction response to the HDMI Source.

In various embodiments, a link initialization may comprise variousstages. A multi-protocol apparatus may be configured (e.g., through asoftware or firmware-based connection manager) to identify the activeHDMI IN adapter and HDMI OUT adapter, and optionally, the plug/unplugevents. A multi-protocol apparatus may be configured (e.g., through theconnection manager) to set and enable paths between the HDMI IN adapterand the HDMI OUT adapter. The source may assert the 5 v signal, and theHDMI IN adapter may pass the indication to the HDMI OUT adapter, whichmay forward it to the sink (unless already done due to 5VO bit). Thesink may respond by asserting HPD. This indication may be forwarded tothe HDMI IN adapter, which may forward it to the source. In variousembodiments, the HDMI IN Adapter may optionally act as a storingrepeater and read the sink before asserting HPD towards the source. Whenthe TMDS link is locked at the HDMI IN adapter, it may send a link_upindication to HDMI OUT adapter (along with the HDMI/DVI state), and TMDSLPK packets and TMU clock sync packets may be sent from this stage. TheHDMI OUT adapter may generate the TMDS clock, and when stable, startdriving TMDS traffic.

When premium content is streamed, the multi-protocol apparatusestunneling HDMI may employ content protection using HDCP. The HDMImapping architecture described herein may support transparent mapping ofpremium content streams over a multi-protocol switching fabric. The HDMImap may appear as an HDMI link directly connecting an HDCP transmitterto an HDCP receiver. The HDCP content protection mechanisms may behandled transparently.

Various embodiments of I/O complexes described herein may be configuredto implement a time synchronization protocol. In various embodiments,the time synchronization protocol may provide a mechanism forsynchronizing the clocks of one or more switches of a multi-protocolswitching fabric.

In various embodiments, a protocol for synchronizing time across aswitching fabric may be a distributed protocol that specifies how thereal-time clocks in an switch domain synchronize with each other. Theclocks may be organized into a master-slave synchronization hierarchywith the clock at the top of the hierarchy (“grandmaster clock”)determining the reference time for the entire domain. Thesynchronization may achieved by exchanging timing messages, with theslaves using the timing information to adjust their clocks to the timeof their master in the hierarchy.

In various embodiments, time sync messages, state machines, and otherentities may be associated with a particular domain. Time establishedwithin one domain by the protocol may be independent of the time inother domains. When multiple domains are inter-connected, an interdomainmaster-slave clock synchronization hierarchy may be established byselecting the grandmaster clock of one domain as the inter-domaingrandmaster clock. The time sync protocol may then synchronize thegrandmaster clocks of other domains to the inter-domain grandmasterclock.

FIG. 20 shows an example time synchronization hierarchy within a singledomain of switches of a multi-protocol switching fabric of various I/Ocomplexes described herein. The time synchronization hierarchy within adomain may be the same as the spanning tree established forconfiguration of the domain. The root switch of the domain may providethe Grandmaster clock for the domain. At every link, the downstreamfacing port may be treated as the master port and the upstream port maybe treated as the slave port from the perspective of the timesynchronization protocol. Each switch, therefore, may contain one slaveport and one or more master ports. In various embodiments, the rootswitch may not contain a slave port as shown.

Multiple domains may be connected together as shown in FIG. 21. Whenmultiple domains are connected together, the default behavior may be tonot synchronize the time across domains. Time synchronization may beenabled across domains by creating an inter-domain master-slavesynchronization hierarchy by selecting one domain to act as theinter-domain grandmaster. The root switch of the selected domain maybecome the inter-domain grandmaster clock. In various embodiments, thetime synchronization protocol may be enabled across an inter-domain linkby configuring one end of the link to be the inter-domain master (IDM)and the other end of the link to be the inter-domain slave (IDS). Invarious embodiments, the inter-domain master-slave synchronizationhierarchy may not contain loops.

In various embodiments, inter-domain links that are not configured (bysoftware, for example) may not participate in the time synchronizationprotocol. As shown in FIG. 21, Domain B is chosen as the inter-domaingrandmaster and the time synchronization protocol is enabled on theinter-domain links A

B, A

D, and A

C. As also shown, inter-Domain time synchronization is not enabled onthe link B

D.

One or more of the switches of a multi-protocol switching fabric mayprovide a free-running oscillator (local clock entity) that is used tocapture timestamps for the time synchronization protocol. In variousembodiments, the free-running oscillator may run at a frequency of 125MHz±100 ppm. A local-time register may be incremented by thefree-running oscillator entity.

Although the timestamps may be captured using the free-runningoscillator, each switch may know the error (both in time and frequency)of the local time relative to the grandmaster time. The time offsetbetween the local time of the free-running oscillator and thegrandmaster time may be represented in a 64-bittime-offset-from-grandmaster register. This register may hold a signedfractional value and use 2's complement representation and may specifytime in nanoseconds multiplied by 216. For example, 2.5 ns may berepresented as 0x0000000000028000. A value of one in all bits, exceptthe most significant, of the field, may indicate that the offset fromgrandmaster time may be too big to be represented. In variousembodiments, the time-offset-from-grandmaster register of the rootswitch (the grandmaster of the domain) may be set to 0 except when thedomain is configured as a slave for inter-domain time synchronization.

In various embodiments, the frequency offset between the free-runningoscillator and the grandmaster clock may be represented in afrequency-offset-from-grandmaster register. This register may specifythe fractional frequency offset and hold a signed fractional valuerepresented using 2's complement notation.

In various embodiments, the time-offset-from-grandmaster register andfrequency-offset-from-grandmaster register may be updated at theconclusion of every time sync packet exchange. Implementations mayattempt to minimize the value of the time offset from the grandmasteralthough this is not required for the time sync protocol operation. Thiscan be done either by tuning the frequency of the free-runningoscillator and/or by adjusting the local-time register.

FIG. 22 shows an example model of a switch assumed by variousembodiments of the time synchronization protocol. As shown, the upstreamport of the switch is the designated slave port while all the downstreamports of the switch are designated as master ports. The local clockentity, which may include the free-running oscillator described herein,and the computation engine may be common to all the ports of the switch.The slave port may provide the timestamp measurements of the computationengine that may enable the computation of the offset of the local timefrom the grandmaster time. The local time value and the computationresults may be made available to all adapter ports of the switch toenable the implementation of any adapter-specific time synchronizationfunctions.

In various embodiments, each master or slave port may contain a protocolengine that may be responsible for processing time synchronizationmessages. Messages used for synchronizing time within a domain mayterminate in the protocol engine of the ports and may not be forwarded.Inter-domain time synchronization messages may be forwarded by theprotocol engine of a receiving master port to the protocol engine of theslave port. The protocol engine of the slave port may be responsible forforwarding the message towards the grandmaster of the domain bytransmitting it towards its link partner.

In various embodiments, the generation of timestamps may be performed bythe physical layer of the ports. The timestamp generation may be donewhen the timestamp point of the synchronization message passes areference plane in the physical layer.

FIG. 23 shows an example timestamp measurement model. In variousembodiments, a timestamp event may be generated at the time oftransmission and reception of a time sync notification ordered set(TSNOS), which may be used to help the time management units (see, e.g.,TMUs of FIGS. 4 and 6) locking an accurate time stamp when transmittingor receiving a TMU packet. The point in the TSNOS between the last bitof the sync character and the first bit of the ordered set data may bereferred to as the timestamp point. In various embodiments, the synccharacter may comprise 2 bits while the ordered set data may comprise 64bits. Within the physical layer, the timestamp may be taken when thetimestamp point passes a reference point called the reference plane. Thereference plane may be permitted to be different for the transmit andreceive paths through the physical layer. In various embodiments, thesame transmit reference plane may be used, however, for all transmittedTSNOS and the same receive reference plane may be used for all receivedTSNOS. In various embodiments, the timestamp measurement has aresolution of at least 8 ns.

FIG. 24 shows an example time sync packet exchange protocol, which maybe used to measure the time offset between the master and slave clocks.In various embodiments, the measurement is only made on the slave portof a switch. As shown in the timing diagram, the time sync packetexchange uses delay request, delay response, and follow up messages.Delay request and delay response messages may be implemented using theTSNOS (described above). The follow up message may be a transport layerpacket.

In various embodiments, the follow up message may be sent by the masterto the slave and may contain timestamps t2 and t3 captured at the masteralong with the current snapshot of the master'stime-offset-from-grandmaster and frequency-offset-from-grandmasterregisters. The time-offset-from-grandmaster andfrequency-offset-from-grandmaster registers of the grandmaster may beencoded as 0 except when inter-domain time synchronization is enabled.

In various embodiments, the transmission rate of the delay requestpackets may be determined by a configuration register of a port of aswitch. The delay response packets may be transmitted as soon aspossible after the receipt of the associated delay request packet.Follow up packets may be transmitted as soon as possible after thetransmission of the associated delay response packet.

In an error occurs during the transmission or reception of any of thetime sync messages, the entire packet exchange cycle may be voided. Anew cycle may then be started after an interval determine by theconfiguration register. The computation of the time offset from thegrandmaster time is described in more detail below.

When two or more domains are connected together, time synchronizationmay be enabled across the inter-domain link by configuring one end ofthe link as the inter-domain slave and the other end as the inter-domainmaster. An example inter-domain time sync protocol is shown in FIG. 25.

As shown in FIG. 25, when time synchronization is enabled, an identicalpacket exchange may occur over the inter-domain link with theinter-domain slave initiating the packet exchange. The computed time andfrequency offsets between the grandmaster clock of the inter-domainslave port and the grandmaster clock of the inter-domain master port maybe passed up the time synchronization hierarchy in the slave domain byusing a transport layer packet called the inter-domain timestamp packet.When the inter-domain timestamp packet reaches the grandmaster (rootswitch) of the slave domain, the time-offset-from-grandmaster andfrequency-offset-from-grandmaster registers in the grandmaster may beupdated with the computed time offset and frequency offset respectivelycontained in the inter-domain timestamp packet. The grandmaster'stime-offset-from-grandmaster and frequency-offset-from-grandmasterregisters may then be passed down the time synchronization hierarchy inthe slave domain in FollowUp packets. This may result in all theswitches in the slave domain synchronizing their time to theinter-domain grandmaster clock.

Various embodiments described herein may provide computation of time andfrequency offsets between a local clock entity on a switch and agrandmaster clock entity on a root switch in a network of switchesconnected together in one or more management domains. In variousembodiments, a time synchronization protocol may include capturing fourtimestamps periodically across a link between two ports (master andslave). Various digital signaling processing operations may be appliedto the timestamps to compute the time and frequency offset of the localclock entity relative to a grandmaster clock. By using digitalsignaling-type and low-pass filtering-type techniques applied to themultiple timestamps described herein, greater accuracy in time and/orfrequency offsets may be obtained, even over larger sized networks ofswitches.

FIG. 26 shows an example topology for time synchronization. As shown,the root switch of the domain i is indicated by using the notation Ri,and master and slave switches in domain i are indicated as Mi and Sirespectively. It is noted that in various embodiments, the same switchwill act as a slave in its upstream port and as a master on all itsdownstream ports, as shown. A switch may also act as an inter-domainmaster or as an inter-domain slave.

Table 1 below shows example definitions of terminology of variousvariables used herein in describing intra-domain time sync computations,inter-domain time sync computations, and grandmaster time computations.

In various embodiments, timestamps may be generated by the physicallayer and may be corrected for asymmetry between transmit and receivepaths. The slave may correct for asymmetry by performing the followingcomputations:t1=delay request sent timestamp+TxTimetoWiret4=delay response received timestamp+RxTimetoWirewhere TxTimetoWire and RxTimetoWire may be configuration registers inthe slave's port configuration space that specify the time durationbetween the instant the timestamp is taken and when the first bit of theTSNOS is received/transmitted on the wire.

In various embodiments, the master may correct for asymmetry byperforming the following computations:t2=delay request received timestamp+RxTimetoWiret3=delay response sent timestamp+TxTimetoWirewhere TxTimetoWire and RxTimetoWire may be configuration registers inthe master's port configuration space that specify the time durationbetween the instant the timestamp is taken and when the first bit of theTSNOS is received/transmitted on the wire. The corrected values t2 andt3 may be sent to the slave in the follow up packet.

For intra-domain sync computations, the frequency ration between themaster's local clock entity and the slave's local clock entity at theconclusion of every nth time sync packet exchange using the followingequation:

  f(S_(i), M_(i))[0] = 1$\mspace{20mu}{{{f\left( {S_{i},M_{i}} \right)}\lbrack 1\rbrack} = \frac{\left( {{t_{1}\lbrack 1\rbrack} - {t_{1}\lbrack 0\rbrack}} \right)}{\left( {{t_{2}\lbrack 1\rbrack} - {t_{2}\lbrack 0\rbrack}} \right)}}$${{f\left( {S_{i},M_{i}} \right)}\lbrack N\rbrack} = {{{f\left( {S_{i},M_{i}} \right)}\left\lbrack {N - 1} \right\rbrack} - \frac{{f\left( {S_{i},M_{i}} \right)}\left\lbrack {N - 1} \right\rbrack}{2^{\alpha}} + \frac{\left( {{t_{1}\lbrack N\rbrack} - {t_{1}\left\lbrack {N - 1} \right\rbrack}} \right)}{2^{\alpha}\left( {{t_{2}\lbrack N\rbrack} - {t_{2}\left\lbrack {N - 1} \right\rbrack}} \right)}}$

TABLE 1 Example Variable Definitions Variable Definition n Refers to then^(th) completed time sync packet exchange between a master and a slave.N Refers to the number of time sync packet exchanges over which thefrequency offset is computed. This value is obtained from theFreqMeasurementWindow register in the time sync device configurationspace. t₁[n] Timestamp in slave's timebase when the Delay Request TSNOSis transmitted. Includes transmit asymmetry corrections at the slave.t₂[n] Timestamp in master's timebase when the Delay Request TSNOS isreceived. Includes receive asymmetry corrections at the master. Thistimestamp is communicated by the master to the slave in the follow uppacket. t₃[n] Timestamp in master's timebase when the Delay ResponseTSNOS is transmitted. Includes transmit asymmetry corrections at themaster. This timestamp is communicated by the master to the slave in thefollow up packet. t₄[n] Timestamp in slave's timebase when the DelayResponse TSNOS is received. Includes receive asymmetry corrections atthe slave. t_(last)(x)[n] Equal to the most recent value of the t₄[n]obtained at the conclusion of a time sync packet exchange between switchx and its master. t_(last-id)(x)[n] Equal to the most recent value ofthe inter-domain timestamp value contained in the follow up packetreceived from switch x's master. This value is computed by aninter-domain slave node in the domain of the switch x's master. S_(i) Atime sync slave in domain i. N_(i) A time sync master in domain i. R_(i)Root switch in domain i. Also the grandmaster of the domain. f(x, y)[n]Average frequency ratio between switch x's LocalClock entity and switchy's LocalClock entity defined by the equation f(x,y) = f_(x)/f_(y) F(x,y)[n] Average frequency offset between switch x's LocalClock entity andswitch y's LocalClock entity defined by the equation F(x,y) = [f(x,y) −1]2⁴¹ D(x, y)[n] Average propagation delay between switch x and switch yexpressed in switch x's timebase. 0(x, y)[n] Average time offset betweenswitch x's LocalClock entity and switch y's LocalClock entity computedrelative to the end of a time sync packet exchange t₄[n]. The timeoffset is defined by the equation 0(x,y) = (Switch x's local time atinstant t₄[n]) − (Switch y's local time at instant t₄[n]). θ(x,y)[n]Average time offset between switch x's LocalClock entity and switch y'sLocalClock entity computed relative to time instant t₃[n]. The timeoffset is defined by the equation θ(x,y) = (Switch x's local time atinstant t₃[n]) − (Switch y's local time at instant t₃[n]). αCo-efficient of the IIR filter used to average the frequency ratio. Thisvalue is obtained from the FreqAvgConst register in the Time Sync deviceconfiguration space. β Co-efficient of the IIR filter used to averagethe propagation delay. This value is obtained from the DelayAvgConstregister in the time sync device configuration space. γ Co-efficient ofthe IIR filter used to average the time offset. This value is obtainedfrom the OffsetAvgConst register in the time sync device configurationspace. δ Co-efficient of the IIR filter used to average the time offseterror. This value is obtained from the ErrorAvgConst register in thetime sync device configuration space.

In various embodiments, the frequency offset between the master's localclock entity and the slave's local clock entity may be computed usingthe equation:F(S _(i) ,M _(i))[N]={f(S _(i) ,M _(i))[N]−1}2⁴¹

In various embodiments, the frequency ration between the slave's localclock entity and the grandmaster's local clock entity may be computedusing the equation:

${{f\left( {S_{i},R_{i}} \right)}\lbrack N\rbrack} = {{{f\left( {S_{i},M_{i}} \right)}\lbrack N\rbrack}\left\{ {1 + \frac{{F\left( {M_{i},R_{i}} \right)}\lbrack N\rbrack}{2^{41}}} \right\}}$

In various embodiments, the frequency offset between the slave's localclock entity and the grandmaster's local clock entity may be computedusing the equation:F(S _(i) ,R _(i))[N]={f(S _(i) ,R _(i))[N]−1}2⁴¹

At the conclusion of time sync packet exchanges, the mean propagationdelay between the slave and the master may be computed using theequation:

$\mspace{20mu}{{{D\left( {M_{i},S_{i}} \right)}\lbrack 0\rbrack} = \frac{\left\{ {\left( {{t_{4}\lbrack 0\rbrack} - {t_{1}\lbrack 0\rbrack}} \right) - \left( {{t_{3}\lbrack 0\rbrack} - {t_{2}\lbrack 0\rbrack}} \right)} \right\}}{2}}$${{D\left( {M_{i},S_{i}} \right)}\lbrack n\rbrack} = {{{D\left( {M_{i},S_{i}} \right)}\left\lbrack {n - 1} \right\rbrack} - \frac{{D\left( {M_{i},S_{i}} \right)}\left\lbrack {n - 1} \right\rbrack}{2^{\beta}} + \frac{\left\{ {\frac{\left( {{t_{4}\lbrack n\rbrack} - {t_{1}\lbrack n\rbrack}} \right)}{{f\left( {S_{i},M_{i}} \right)}\lbrack N\rbrack}\left( {{t_{3}\lbrack n\rbrack} - {t_{3}\lbrack n\rbrack}} \right)} \right\}}{2^{({\beta + 1})}}}$

At the conclusion of time sync packet exchanges, the time offset(0(S_(i),M_(i))[n]) between the slave and the master may be computedusing the following equations:

  W(S_(i), M_(i))[0] = (t₃[0] − t₄[0] + D(M_(i), S_(i))[0])${{W\left( {S_{i},M_{i}} \right)}\lbrack n\rbrack} = {{{W\left( {S_{i},M_{i}} \right)}\left\lbrack {n - 1} \right\rbrack} - \frac{{W\left( {S_{i},M_{i}} \right)}\left\lbrack {n - 1} \right\rbrack}{2^{\gamma}} + \frac{\left( {{t_{3}\lbrack n\rbrack} - {t_{4}\lbrack n\rbrack} + {{D\left( {M_{i},S_{i}} \right)}\lbrack n\rbrack}} \right)}{2^{\gamma}}}$  E(S_(i), M_(i))[0] = 0${{E\left( {S_{i},M_{i}} \right)}\lbrack n\rbrack} = {{{E\left( {S_{i},M_{i}} \right)}\left\lbrack {n - 1} \right\rbrack} - \frac{{E\left( {S_{i},M_{i}} \right)}\left\lbrack {n - 1} \right\rbrack}{2^{\delta}} + \frac{\left( {{{W\left( {S_{i},M_{i}} \right)}\lbrack n\rbrack} - {t_{3}\lbrack n\rbrack} + {t_{4}\lbrack n\rbrack} - {{D\left( {M_{i},S_{i}} \right)}\lbrack n\rbrack}} \right)}{2^{\delta}}}$  O(S_(i), M_(i))[n] = W(S_(i), M_(i))[n] − E(S_(i), M_(i))[n]

In various embodiments, the time offset of the master clock from thegrandmaster clock that may be sent in the follow up packet by the mastermay be computed using the following equation:

${{\Theta\left( {M_{i},R_{i}} \right)}\lbrack n\rbrack} = {{{O\left( {M_{i},R_{i}} \right)}\lbrack n\rbrack} - \frac{{{F\left( {M_{i},R_{i}} \right)}\lbrack N\rbrack}\left\{ {{t_{3}\lbrack n\rbrack} - {{t_{last}\left( M_{i} \right)}\lbrack n\rbrack}} \right\}}{\left\{ {2^{41} + {{F\left( {M_{i},R_{i}} \right)}\lbrack N\rbrack}} \right\}}}$

In various embodiments, the time offset between the slave clock and thegrandmaster clock may be computed using the following equation:

${{O\left( {S_{i},R_{i}} \right)}\lbrack n\rbrack} = {{{O\left( {S_{i},M_{i}} \right)}\lbrack n\rbrack} + {{\Theta\left( {M_{i},R_{i}} \right)}\lbrack n\rbrack} - \frac{{{D\left( {M_{i},S_{i}} \right)}\lbrack n\rbrack}{{F\left( {M_{i},R_{i}} \right)}\lbrack N\rbrack}}{\left\{ {2^{41} + {{F\left( {M_{i},R_{i}} \right)}\lbrack N\rbrack}} \right\}}}$

Various computational techniques may also be used for inter-domainconnections between an inter-domain master and an inter-domain slaveconnected by an inter-domain link for time sync packet exchanges.

In various embodiments, at the conclusion of inter-domain packetexchanges, an inter-domain slave may be configured to compute the valueof the inter-domain timestamp using the formula:

${{t_{{last}\text{-}{id}}\left( S_{i} \right)}\lbrack n\rbrack} = {{{t_{last}\left( S_{i} \right)}\lbrack n\rbrack} + {{O\left( {S_{i},R_{i}} \right)}\lbrack n\rbrack} + \frac{\left( {{t_{4}\lbrack n\rbrack} - {{t_{last}\left( S_{i} \right)}\lbrack n\rbrack}} \right)}{\left( {1 + \frac{{F\left( {S_{i},R_{i}} \right)}\lbrack N\rbrack}{3^{41}}} \right)}}$wherein the subscript i refers to the slave domain, the subscript jrefers to the master domain, and the subscript g refers to thegrandmaster domain. The timestamp t₄[n] may refer to the value obtainedat the conclusion of the inter-domain time sync exchange. The computedvalue of t_(last-id)(S_(i))[n] may be sent by the inter-domain slavenode in the inter-domain timestamp packet.

In various embodiments, at the conclusion of every nth time sync packetexchange, the frequency ratio between the inter-domain master's localclock entity and the inter-domain slave's local clock entity may becomputed using the equations:

  f(S_(i), M_(j))[0] = 1$\mspace{20mu}{{{f\left( {S_{i},M_{j}} \right)}\lbrack 1\rbrack} = \frac{\left( {{t_{1}\lbrack 1\rbrack} - {t_{1}\lbrack 0\rbrack}} \right)}{\left( {{t_{2}\lbrack 1\rbrack} - {t_{2}\lbrack 0\rbrack}} \right)}}$${{f\left( {S_{i},M_{j}} \right)}\lbrack N\rbrack} = {{{f\left( {S_{i},M_{j}} \right)}\left\lbrack {N - 1} \right\rbrack} - \frac{{f\left( {S_{i},M_{j}} \right)}\left\lbrack {N - 1} \right\rbrack}{2^{\alpha}} + \frac{\left( {{t_{1}\lbrack N\rbrack} - {t_{1}\left\lbrack {N - 1} \right\rbrack}} \right)}{2^{\alpha}\left( {{t_{2}\lbrack N\rbrack} - {t_{2}\left\lbrack {N - 1} \right\rbrack}} \right)}}$

In various embodiments, the frequency offset between the inter-domainmaster's local clock entity and the inter-domain slave's local clockentity may be computed using the equations:F(S _(i) ,M _(j))[N]={f(S _(i) ,M _(j))[N]−1}2⁴¹

In various embodiments, the frequency ratio between the root switch of aslave domain and the root switch of a grandmaster domain may be computedusing the following equation:

${{f\left( {R_{i},R_{g}} \right)}\lbrack N\rbrack} = \frac{{{f\left( {S_{i},M_{j}} \right)}\lbrack N\rbrack}\left\{ {1 + \frac{{F\left( {M_{j},R_{j}} \right)}\lbrack N\rbrack}{2^{41}}} \right\}\left\{ {1 + \frac{{F\left( {R_{j},R_{g}} \right)}\lbrack N\rbrack}{2^{41}}} \right\}}{{f\left( {S_{i},R_{i}} \right)}\lbrack N\rbrack}$

In various embodiments, the frequency offset between the root switch ofa slave domain and the root switch of a grandmaster domain may becomputed using the following equation:F(R _(i) ,R _(g))[N]={f(R _(i) ,R _(g))[N]−1}2⁴¹

At the conclusion of time sync packet exchanges, the mean propagationdelay between an inter-domain slave and an inter-domain master may becomputed using the following equation:

$\mspace{20mu}{{{D\left( {M_{j},S_{i}} \right)}\lbrack 0\rbrack} = \frac{\left\{ {\left( {{t_{4}\lbrack 0\rbrack} - {t_{1}\lbrack 0\rbrack}} \right) - \left( {{t_{3}\lbrack 0\rbrack} - {t_{2}\lbrack 0\rbrack}} \right)} \right\}}{2}}$${{D\left( {M_{j},S_{i}} \right)}\lbrack n\rbrack} = {{{D\left( {M_{j},S_{i}} \right)}\left\lbrack {n - 1} \right\rbrack} - \frac{{D\left( {M_{j},S_{i}} \right)}\left\lbrack {n - 1} \right\rbrack}{2^{\beta}} + \frac{\left\{ {\frac{\left( {{t_{4}\lbrack n\rbrack} - {t_{1}\lbrack n\rbrack}} \right)}{{f\left( {S_{i},M_{j}} \right)}\lbrack N\rbrack}\left( {{t_{3}\lbrack n\rbrack} - {t_{2}\lbrack n\rbrack}} \right)} \right\}}{2^{({\beta + 1})}}}$

At the conclusion of time sync packet exchanges, the time offset(0(S_(i),M_(j))[n]) between an inter-domain slave and an inter-domainmaster may be computed using the following equation:

$\mspace{20mu}{{{W\left( {S_{i},M_{j}} \right)}\lbrack 0\rbrack} = \frac{\left( {{t_{3}\lbrack 0\rbrack} - {t_{4}\lbrack 0\rbrack} + {{D\left( {M_{j},S_{i}} \right)}\lbrack 0\rbrack}} \right)}{2}}$${{W\left( {S_{i},M_{j}} \right)}\lbrack n\rbrack} = {{{W\left( {S_{i},M_{j}} \right)}\left\lbrack {n - 1} \right\rbrack} - \frac{{W\left( {S_{i},M_{j}} \right)}\left\lbrack {n - 1} \right\rbrack}{2^{\gamma}} + \frac{\left( {{t_{3}\lbrack n\rbrack} - {t_{4}\lbrack n\rbrack} + {{D\left( {M_{j},S_{i}} \right)}\lbrack n\rbrack}} \right)}{2^{\gamma}}}$${{E\left( {S_{i},M_{j}} \right)}\lbrack n\rbrack} = {{{E\left( {S_{i},M_{j}} \right)}\left\lbrack {n - 1} \right\rbrack} - \frac{{E\left( {S_{i},M_{j}} \right)}\left\lbrack {n - 1} \right\rbrack}{2^{\delta}} + \frac{\left( {{{W\left( {S_{i},M_{j}} \right)}\lbrack n\rbrack} - {t_{3}\lbrack n\rbrack} + {t_{4}\lbrack n\rbrack} - {{D\left( {M_{j},S_{i}} \right)}\lbrack n\rbrack}} \right)}{2^{\delta}}}$  O(S_(i), M_(j))[n] = W(S_(i), M_(j))[n] − E(S_(i), M_(j))[n]

In various embodiments, the time offset of an inter-domain master clock(M_(j)) from the root switch clock (R_(j)) of its domain that may besent in a follow up packet by the inter-domain master may be computedusing the following equation:

${{\Theta\left( {M_{j},R_{j}} \right)}\lbrack n\rbrack} = {{{O\left( {M_{j},R_{j}} \right)}\lbrack n\rbrack} - \frac{{{F\left( {M_{j},R_{j}} \right)}\lbrack N\rbrack}\left\{ {{t_{3}\lbrack n\rbrack} - {{t_{last}\left( M_{j} \right)}\lbrack n\rbrack}} \right\}}{\left\{ {2^{41} + {{F\left( {M_{j},R_{j}} \right)}\lbrack N\rbrack}} \right\}}}$

In various embodiments, the time offset of an inter-domain slave's clock(S_(i)) from the root switch clock of a master domain (R_(j)) may becomputed using the following equation:

${{O\left( {S_{i},R_{j}} \right)}\lbrack n\rbrack} = {{{O\left( {S_{i},M_{j}} \right)}\lbrack n\rbrack} + {{\Theta\left( {M_{j},R_{j}} \right)}\lbrack n\rbrack} - \frac{{{D\left( {M_{j},S_{i}} \right)}\lbrack n\rbrack}{{F\left( {M_{j},R_{j}} \right)}\lbrack N\rbrack}}{\left\{ {2^{41} + {{F\left( {M_{j},R_{j}} \right)}\lbrack N\rbrack}} \right\}}}$

In various embodiments, the time offset of the root switch of a slavedomain (R_(j)) and the root switch of a grandmaster domain (R_(g)) maybe computed using the following equation:

${{O\left( {R_{i},R_{g}} \right)}\lbrack n\rbrack} = {{{O\left( {S_{i},R_{j}} \right)}\lbrack n\rbrack} + {{O\left( {R_{j},R_{g}} \right)}\lbrack n\rbrack} - {{O\left( {S_{i},R_{i}} \right)}\lbrack n\rbrack} + \frac{{{F\left( {S_{i},R_{i}} \right)}\lbrack N\rbrack}\left\{ {{t_{4}\lbrack n\rbrack} - {{t_{last}\left( S_{i} \right)}\lbrack n\rbrack}} \right\}}{\left\{ {2^{41} + {{F\left( {S_{i},R_{i}} \right)}\lbrack N\rbrack}} \right\}} - \frac{{{F\left( {R_{j},R_{g}} \right)}\lbrack N\rbrack}\left\{ {{t_{4}\lbrack n\rbrack} + {{O\left( {S_{i},R_{j}} \right)}\lbrack n\rbrack} - {{t_{{last}\text{-}{id}}\left( M_{j} \right)}\lbrack n\rbrack}} \right\}}{\left\{ {2^{41} + {{F\left( {R_{j},R_{g}} \right)}\lbrack N\rbrack}} \right\}}}$wherein, in various embodiments, if the master domain j is the same asthe grandmaster domain g, the values of 0(R_(j),R_(g))[n],F(R_(j),R_(g))[N], and t_(last-id)(M_(i))[n] may be assumed to be 0

At any instant of time t, any switch (S_(i)) in a domain i may becapable of computing a grandmaster time t_(g), using the followingequations:

$t_{g} = {{{t_{{last}\text{-}{id}}\left( S_{i} \right)}\lbrack n\rbrack} + {{O\left( {R_{i},R_{g}} \right)}\lbrack n\rbrack} + \frac{\left\{ {{{t_{last}\left( S_{i} \right)}\lbrack n\rbrack} + {{O\left( {S_{i},R_{i}} \right)}\lbrack n\rbrack} + \frac{\left( {t - {{t_{last}\left( S_{i} \right)}\lbrack n\rbrack}} \right)}{\left( {1 + \frac{{F\left( {S_{i},R_{i}} \right)}\lbrack N\rbrack}{2^{41}}} \right)} - {{t_{{last}\text{-}{id}}\left( S_{i} \right)}\lbrack n\rbrack}} \right\}}{\left\{ {1 + \frac{{F\left( {R_{i},R_{g}} \right)}\lbrack N\rbrack}{2^{41}}} \right\}}}$wherein, in various embodiments, if the domain i is not slaved to anyother domain the values of t_(last-id)(S_(i))[n], 0(R_(i),R_(g))[n], andF(R_(i),R_(g))[N], and may be assumed to be 0.

FIG. 27 is a flow diagram of an example method 2700 for configuring amulti-protocol tunneling I/O interconnect, in accordance with variousembodiments of the present disclosure. The method 2700 may include oneor more functions, operations, or actions as is illustrated by blocks2702-2710.

Processing for the method 2700 may start with block 2702 by identifyinga plurality of switches of a switching fabric of a multi-protocolinterconnect.

The method 2700 may proceed to block 2704 by creating a spanning treerepresentation of the plurality of switches.

The method 2700 may proceed to block 2706 by assigning uniqueidentifications (IDs) to the switches of plurality of switches of thespanning tree. In various embodiments, the IDs may represent therelative positions of the switches within the spanning tree.

The method 2700 may proceed to block 2708 by storing the IDs and depthof the switches (in the spanning tree) in one or more registers of eachof the switches.

The method 2700 may proceed to block 2710 by routing configurationpackets through the spanning tree to the switches based at least in parton their respective IDs.

FIG. 28 illustrates an example method for operating a computer apparatusincluding a multi-protocol tunneling I/O interconnect, in accordancewith various embodiments of the present disclosure. The method 2800 mayinclude one or more functions, operations, or actions as is illustratedby blocks 2802-2822.

Processing for the method 2800 may start with block 2802 by determiningwhether a peripheral device has been plugged into anon-protocol-specific port of a computer apparatus including amulti-protocol tunneling I/O interconnect. Plugging may refer to aperipheral device being directly coupled with the non-protocol-specificport and/or a target peripheral device being directly coupled to someother peripheral device directly coupled with the non-protocol-specificport. In the latter embodiments, one or more other peripheral devicesmay be operatively disposed between the target peripheral device and thenon-protocol-specific port. If no peripheral device has been plugged,then processing in block 2802 may repeat. In various embodiments, thecomputer apparatus may be configured to issue an interrupt signalindicating when a peripheral device has been plugged (e.g.,hot-plugged).

Processing for the method 2800 may proceed to block 2804 by determiningwhether a data packet has been received. If no data packet has beenreceived, then processing in block 2804 may repeat. In variousembodiments, a data packet may be received from the peripheral device orfrom within the computer apparatus. In various embodiments, data packetswithin the computer apparatus may be received by the multi-protocoltunneling I/O interconnect from a protocol-specific controller (“hostprotocol-specific controller”) of the computer apparatus.

Processing for the method 2800 may proceed to block 2806 by determiningwhether the data packet was received from the peripheral device or froma host protocol-specific controller. If no data packet has beenreceived, then processing in block 2806 may repeat.

If the data packet was received from the peripheral device, processingfor the method 2800 may proceed to block 2808 by encapsulating packetsof a first protocol into first transport layer packets configured to berouted through the switching fabric of the I/O interconnect. In variousembodiments, packets of a second protocol, different from the firstprotocol, may also be encapsulated into second transport layer packetsfor routing through the switching fabric.

Processing for the method 2800 may proceed to block 2810 bysimultaneously routing the first and second transport layer packetsthrough the switching fabric of the I/O interconnect.

Processing for the method 2800 may proceed to block 2812 bydecapsulating the transport layer packets. In various embodiments,decapsulation may be performed an adapter port of a switch of theswitching fabric.

Processing for the method 2800 may proceed to block 2814 by routing thedecapsulated packets to different host protocol-specific controllers ofthe computer apparatus.

If the data packet was received from the peripheral device, processingfor the method 2800 may proceed from block 2806 to block 2816 byencapsulating packets of a first protocol into first transport layerpackets configured to be routed through the switching fabric of the I/Ointerconnect. In various embodiments, packets of a second protocol,different from the first protocol, may also be encapsulated into secondtransport layer packets for routing through the switching fabric.

Processing for the method 2800 may proceed to block 2818 bysimultaneously routing the first and second transport layer packetsthrough the switching fabric of the I/O interconnect.

Processing for the method 2800 may proceed to block 2820 bydecapsulating the transport layer packets. In various embodiments,decapsulation may be performed an adapter port of a switch of theswitching fabric.

Processing for the method 2800 may proceed to block 2822 by routing thedecapsulated packets to a peripheral device via a non-protocol-specificport of the computer apparatus.

FIG. 29 illustrates an example method for time synchronization of amulti-protocol interconnect, in accordance with various embodiments ofthe present disclosure. The method 2900 may include one or morefunctions, operations, or actions as is illustrated by blocks 2902-2910.

Processing for the method 2900 may start with block 2902 by providing afirst local time of a first switch of a switching fabric of amulti-protocol interconnect to a second switch of the switching fabric.In various embodiments, the first local time may be provided from a portof the first switch to a port of the second switch. In variousembodiments, the switches may be in the same domain or differentdomains.

Processing for the method 2900 may proceed to block 2904 by determininga second local time of the second switch. In various embodiments, thesecond local time may be based at least in part on a timestamp of afree-running oscillator of the second switch.

Processing for the method 2900 may proceed to block 2906 by calculatingan offset value based at least in part on the first local time and thesecond local time. In various embodiments, the offset value based atleast in part on the timestamp of the free-running oscillator of thesecond switch and the first local time received from the first switch.

Processing for the method 2900 may proceed to block 2908 by providingthe offset value and the second local time to one or more ports of thesecond switch.

Processing for the method 2900 may proceed to block 2910 by providingthe first local time from the second switch to a third switch of theswitching fabric. The third switch may be in the same domain as thefirst switch and/or the second switch or a different domain from eitherof the first switch and second switch. Although not shown, a third localtime of the third switch may be adjusted to the first local time. Forembodiments, in which the third switch is a slave switch within a seconddomain, the third switch may provide the first local time to a fourthswitch in the second domain, and a fourth local time of the fourthswitch may be adjusted to the first local time. The adjusted fourthlocal time may then be provided back to the third switch or anotherswitch in the second domain for time synchronization.

In various embodiments, an article of manufacture may be employed toimplement one or more methods as disclosed herein. FIG. 30 describes anexample article of manufacture 3000. As shown, the article ofmanufacture 3000 may include a computer-readable non-transitory storagemedium 3002 and a storage medium 3002. The storage medium 3002 mayinclude programming instructions 3004 configured to cause an apparatusto practice some or all aspects of multi-protocol tunneling, inaccordance with embodiments of the present disclosure.

The storage medium 3002 may represent a broad range of persistentstorage medium known in the art, including but not limited to flashmemory, optical disks or magnetic disks. The programming instructions3004, in particular, may enable an apparatus, in response to theirexecution by the apparatus, to perform various operations describedherein. For example, the storage medium 3002 may include programminginstructions 3004 configured to cause an apparatus to practice some orall aspects of multi-protocol tunneling of the methods of FIGS. 27-29,for example, in accordance with embodiments of the present disclosure.

Although various example methods, apparatus, systems, and articles ofmanufacture have been described herein, the scope of coverage of thepresent disclosure is not limited thereto. On the contrary, the presentdisclosure covers all methods, apparatus, and articles of manufacturefairly falling within the scope of the appended claims either literallyor under the doctrine of equivalents. For example, although the abovediscloses example systems including, among other components, software orfirmware executed on hardware, it should be noted that such systems aremerely illustrative and should not be considered as limiting. Inparticular, it is contemplated that any or all of the disclosedhardware, software, and/or firmware components could be embodiedexclusively in hardware, exclusively in software, exclusively infirmware or in some combination of hardware, software, and/or firmware.

What is claimed is:
 1. An integrated circuit device comprising a firstswitch including a first port coupled to a switching structure, a secondswitch including a second port coupled to the first port to enable dataexchange through the switching structure, the first port to: transmit afirst time sync packet to the second port, the first time sync packetcorresponding to a first timestamp of the first switch, receive a secondtime sync packet from the second port, the second time sync packetcorresponding to a third timestamp of the second switch, determine atthe first port a fourth timestamp of the first switch corresponding toreceipt of the second time sync packet from the second port, and receivea follow up time sync packet from the second port, the follow up timesync packet corresponding to a second timestamp of the second switch andcorresponding to receipt at the second port of the first time syncpacket, and a time management unit to calculate a time offset betweenthe first switch and the second switch based at least in part on acalculation with the first, second, third, and fourth timestamps,including to synchronize the time based on a delay between thetimestamps of the second switch and the timestamps of the first switch,and to account for asymmetry between a transmit path and a receive pathbetween the first and second ports.
 2. The integrated circuit device ofclaim 1 wherein the time management unit further comprises afree-running oscillator as a clock local to the first switch to generatethe first and fourth timestamps.
 3. The integrated circuit device ofclaim 1 wherein the second switch is coupled to exchange data with aroot switch separate from the first and second switches, the root switchhigher up a network hierarchy than the first and second switches, andwherein the follow up time sync packet further comprises a time offsetto indicate a time difference between the second switch and the rootswitch, wherein the time management unit further to calculate the timebased at least in part on the time offset.
 4. The integrated circuitdevice of claim 3 wherein the time management unit is to calculate thetime including an adjustment to a time of the root switch.
 5. Theintegrated circuit device of claim 1 wherein the first and the fourthtimestamps are generated at a physical layer of the port.
 6. Theintegrated circuit device of claim 1 wherein the integrated circuitdevice is configured for a multiprotocol switching fabric tocommunicatively couple a computer with a plurality of peripheraldevices, wherein the multiprotocol switching fabric to transmit dataaccording to a first protocol and a second protocol different from thefirst protocol, the computer to exchange data of the first and secondprotocols.
 7. The integrated circuit device of claim 6 wherein the firstand the second protocols are selected from PCI Express, USB,DisplayPort, or HDMI, or a combination.
 8. A method for adjusting alocal time on a device comprising: transmitting a first time sync packetfrom a first port of a first switch to a second port of a second switch,the first time synch packet corresponding to a first timestamp of thefirst switch, receiving at the first port a second time sync packet fromthe second port, the second time sync packet corresponding to a thirdtimestamp of the second switch, determining at the first port a fourthtimestamp of the first switch corresponding to receipt of the secondtime sync packet from the second port, receiving at the first port afollow up time sync packet from the second port, the follow up time syncpacket corresponding to a second timestamp of the second switch andcorresponding to receipt at the second port of the first time syncpacket, and adjusting a time value at the first switch based at least inpart on a calculation with the first, second, third, and fourthtimestamps, including synchronizing the time value based on a delaybetween the timestamps of the second switch and the timestamps of thefirst switch, including accounting for asymmetry between a transmit pathand a receive path between the first and second ports.
 9. The method ofclaim 8 wherein the second switch is coupled to exchange data with aroot switch separate from the first and second switches, and wherein thefollow up time sync packet further comprises a time offset to indicate atime difference between the second switch and the root switch of adomain of switches, wherein adjusting the time value at the first switchis based additionally on the time offset.
 10. The method of claim 8wherein the second switch is coupled to exchange data with a root switchseparate from the first and second switches, and wherein the follow uptime sync packet further comprises a frequency offset from the rootswitch of a domain of switches to indicate a clock frequency differencebetween the second switch and the root switch wherein adjusting the timevalue at the first switch is based additionally on the frequency offsetvalue.
 11. The method of claim 8 additionally comprising correcting thefirst and the fourth timestamps for asymmetry between transmit andreceive paths, respectively, for the first switch.
 12. The method ofclaim 8 additionally comprising correcting the second and the thirdtimestamps for asymmetry between receive and transmit paths,respectively, for the second switch.
 13. The method of claim 8additionally comprising determining a mean propagation delay between thefirst port and the second port and adjusting a time value at the firstswitch at least in part on the first, second, third, and fourthtimestamps and on the mean propagation delay between the first switchand the second switch.
 14. The method of claim 9 wherein the time valueat the first switch is adjusted to a time value of the root switch. 15.The method of claim 10 wherein the time value at the first switch isadjusted to a time value of the root switch.
 16. The method of claim 8wherein the first and the second switches are part of a multiprotocolswitching fabric to communicatively couple a computer with a pluralityof peripheral devices, wherein the multiprotocol switching fabric totransmit data according to a first protocol and a second protocoldifferent from the first protocol, the computer to exchange data of thefirst and second protocols.
 17. The method of claim 16 wherein the firstand the second protocols are selected from PCI Express, USB,DisplayPort, or HDMI, or a combination.
 18. A system comprising: aprocessor and integrated circuit device wherein the integrated circuitdevice is operably coupled to the processor wherein the integratedcircuit device comprises: a first switch including a first port coupledto a switching structure, a second switch including a second portcoupled to the first port to enable data exchange through the switchingstructure, the second port to: receive a first time sync packet at thefirst port of the plurality of ports from the first port, the first timesync packet corresponding to a first timestamp of the first switch, senda second time sync packet to the first port, the second time sync packetcorresponding to a third timestamp of the second switch, and send afollow up time sync packet to the first port, the follow up time syncpacket corresponding to a second timestamp of the second switch andcorresponding to receipt at the second port of the first time syncpacket, a second time management unit comprising a local clock at thesecond switch, the second and third timestamps associated with a time ofthe local clock of the second switch; and a first time management unitcomprising a local clock at the first switch, the first timestampassociated with a time of the local clock of the first switch, andfurther comprising a fourth timestamp associated with the time of thelocal clock of the first switch, corresponding to receipt of the secondtime sync packet at the first port, the first time management unit tocalculate a synchronization time offset between the first switch and thesecond switch based at least in part on a calculation with the first,second, third, and fourth timestamps, including to synchronize the timebased on a delay between the timestamps of the second switch and thetimestamps of the first switch, and to account for asymmetry between atransmit path and a receive path between the first and second ports. 19.The system of claim 18 wherein the local clock comprises a free-runningoscillator local to the first switch to generate the first and fourthtimestamps.
 20. The system of claim 18 wherein the first and the secondtimestamps are generated at a physical layer of the first port.
 21. Thesystem of claim 18 wherein the integrated circuit device is configuredfor a multiprotocol switching fabric to communicatively couple acomputer with a plurality of peripheral devices, wherein themultiprotocol switching fabric to transmit data according to a firstprotocol and a second protocol different from the first protocol, thecomputer to exchange data of the first and second protocols.
 22. Thesystem of claim 21 wherein the first and the second protocols areselected from PCI Express, USB, DisplayPort, or HDMI, or a combination.23. The system of claim 18, wherein the system is a desktop computer, alaptop computer, a handheld computer, a tablet computer, a netbookcomputer, a server, a set-top box, a digital recorder, a game console, asmart phone, a personal digital assistant, a mobile phone, a digitalmedia player, or a digital camera.
 24. A system comprising: a processorand integrated circuit device wherein the integrated circuit device isoperably coupled to the processor wherein the integrated circuit devicecomprises: a first integrated circuit switch including a first portcoupled to a switching structure, a second integrated circuit switchincluding a second port coupled to the first port to enable dataexchange through the switching structure, the first port to: transmit afirst time sync packet to the second port, the first time sync packetcorresponding to a first timestamp of the first integrated circuitswitch, receive a second time sync packet rom the second port, thesecond time sync packet corresponding to a third timestamp of the secondintegrated circuit switch, determine at the first port a fourthtimestamp of the first integrated circuit switch corresponding toreceipt of the second time sync packet from the second port, and receivea follow up time sync packet from the second port, the follow up timesync packet corresponding to a second timestamp of the second integratedcircuit switch and corresponding to receipt at the second port of thefirst time sync packet, and a time management unit to calculate a timeoffset between the first switch and the second switch based at least inpart on a calculation with the first, second, third, and fourthtimestamps, including to synchronize the time based on a delay betweenthe timestamps of the second integrated circuit switch and thetimestamps of the first integrated circuit switch, and to account forasymmetry between a transmit path and a receive path between the firstand second ports.
 25. The system of claim 24 wherein the time managementunit further comprises a free-running oscillator as a clock local to thefirst switch to generate the first and fourth timestamps.
 26. The systemof claim 24 wherein the second switch is coupled to exchange data with aroot switch separate from the first and second switches, the root switchhigher up a network hierarchy than the first and second switches, andwherein the follow up time sync packet further comprises a time offsetto indicate a time difference between the second switch and the rootswitch, wherein the time management unit further to calculate the timebased at least in part on the time offset.
 27. The system of claim 26wherein the time management unit is to calculate the time including anadjustment to a time of the root switch.
 28. The system of claim 24wherein the first and the fourth timestamps are generated at a physicallayer of the port.
 29. The system of claim 24 wherein the integratedcircuit device additionally comprises one or more adapter ports and theadapter ports are capable of time synchronization functions that arebased in part on the time determined by the time management unit. 30.The system of claim 27 wherein the integrated circuit deviceadditionally comprises one or more adapter ports and the adapter portsare capable of time synchronization functions that are based in part onthe time that is adjusted to the time of the root switch.
 31. The systemof claim 24 wherein the integrated circuit device is configured for amultiprotocol switching fabric to communicatively couple a computer witha plurality of peripheral devices, wherein the multiprotocol switchingfabric to transmit data according to a first protocol and a secondprotocol different from the first protocol, the computer to exchangedata of the first and second protocols.
 32. The system of claim 31wherein the first and the second protocols are selected from PCIExpress, USB, DisplayPort, or HDMI, or a combination.
 33. The system ofclaim 24, wherein the system is a desktop computer, a laptop computer, ahandheld computer, a tablet computer, a netbook computer, a server, aset-top box, a digital recorder, a game console, a smart phone, apersonal digital assistant, a mobile phone, a digital media player, or adigital camera.